Package on package devices and methods of packaging semiconductor dies

ABSTRACT

Package on package (PoP) devices and methods of packaging semiconductor dies are disclosed. In one embodiment, a PoP device includes a first packaged die and a second packaged die coupled to the first packaged die. Metal pillars are coupled to the first packaged die. The metal pillars have a first portion proximate the first packaged die and a second portion disposed over the first portion. Each of the metal pillars is coupled to a solder joint proximate the second packaged die.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as personal computers, cell phones, digital cameras, and otherelectronic equipment, as examples. Semiconductor devices are typicallyfabricated by sequentially depositing insulating or dielectric layers,conductive layers, and semiconductive layers of material over asemiconductor substrate, and patterning the various material layersusing lithography to form circuit components and elements thereon.

The semiconductor industry continues to improve the integration densityof various electronic components (e.g., transistors, diodes, resistors,capacitors, etc.) by continual reductions in minimum feature size, whichallow more components to be integrated into a given area. These smallerelectronic components also require smaller packages that utilize lessarea than packages of the past, in some applications.

Package on package (PoP) technology is becoming increasingly popular forits ability to allow for denser integration of integrated circuits intoa small overall package. PoP technology is employed in many advancedhandheld devices, such as smart phones, for example.

Improved PoP packaging techniques are needed in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a cross-sectional view of a method of attaching a toppackaged die to a bottom packaged die having a plurality of metalpillars disposed thereon in accordance with an embodiment of the presentdisclosure;

FIG. 2 is a cross-sectional view of a PoP device packaged in accordancewith the method shown in FIG. 1;

FIG. 3 shows a cross-sectional view of a PoP device packaged inaccordance with another embodiment, wherein the metal pillars aredisposed on the top packaged die;

FIG. 4 is a cross-sectional view of a PoP device packaged in accordancewith another embodiment, wherein metal pillars are disposed on both thetop and bottom packaged dies;

FIG. 5 illustrates a cross-sectional view of a PoP device packaged inaccordance with yet another embodiment, wherein the metal pillarscomprise a cone or ladder shape;

FIG. 6 is a more detailed view of a ladder-shaped metal pillar shown inFIG. 5;

FIG. 7 shows a cross-sectional view of a PoP device packaged inaccordance with another embodiment, wherein the metal pillars comprise asocket shape;

FIG. 8 is a cross-sectional view of a PoP device packaged in accordancewith yet another embodiment, wherein the metal pillars comprise theshape of the letter “I”;

FIGS. 9 through 13 illustrate cross-sectional views of a method offorming the metal pillars at various stages using a two-step platingprocess in accordance with an embodiment of the present disclosure;

FIGS. 14 and 15 are cross-sectional views of an example of a method offorming a second layer of photoresist over a first layer of photoresistand a first portion of the metal pillars in accordance with embodimentsof the present disclosure;

FIGS. 16 through 18 illustrate cross-sectional views of methods offorming a protection layer over the metal pillars and forming a moldingcompound over the metal pillars and a bottom die in accordance with anembodiment;

FIGS. 19 through 21 show cross-sectional views of methods of forming themolding compound over the metal pillars and the bottom die, and openingthe molding compound over the metal pillars so that electricalconnections can be made to the metal pillars in accordance withembodiments of the present disclosure;

FIG. 22 shows a more detailed view of an cambered opening over a metalpillar shown in FIG. 21;

FIGS. 23 and 24 illustrate laser drilling calculations of various anglesthat may be used to determine the angle of the cambered opening shown inFIG. 22 based on solder ball dimensions and metal pillar width;

FIGS. 25 and 26 show cross-sectional views of methods of opening themolding compound over the metal pillars in accordance with otherembodiments;

FIG. 27 is an example of a top packaged die in accordance with anembodiment that includes a plurality of top dies packaged over a topsubstrate; and

FIG. 28 is a flow chart illustrating a method of packaging multiplesemiconductor dies in accordance with an embodiment of the presentdisclosure.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the present disclosure arediscussed in detail below. It should be appreciated, however, that thepresent disclosure provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the disclosure, and do not limit the scope of the disclosure.

Embodiments of the present disclosure are related to packaging ofsemiconductor devices. Novel packaging structures and methods ofpackaging multiple semiconductor devices in PoP packages will bedescribed herein. Note that for simplification, not all element numbersare included in each subsequent drawing; rather, the element numbersmost pertinent to the description of each drawing are included in eachof the drawings.

FIG. 1 illustrates a cross-sectional view of a method of attaching asecond (or top) packaged die 140 to a first (or bottom) packaged die 120having a plurality of metal pillars 102 disposed thereon in accordancewith an embodiment of the present disclosure. A first die 110 ispackaged to form the first packaged die 120, and at least one second die128 is packaged to form a second packaged die 140. The second packageddie 140 is then packaged with the first packaged die 120 by attachingsolder balls 132 on the bottom surface 124 of the second packaged die140 to the metal pillars 102 on the top surface 101 of the firstpackaged die 120, forming a PoP device 142, as shown in FIG. 2, which isa cross-sectional view of a PoP device 142 packaged in accordance withthe method shown in FIG. 1.

Referring to FIG. 1, to package the first die 110, the first die 110 isattached to a substrate 100. First, a first substrate 100 is provided.Only one first substrate 100 is shown in the drawings; however, severalfirst substrates 100 are processed on a workpiece comprising a pluralityof first substrates 100, and the workpiece is later singulated, afterpackaging first dies 110 on the first substrates 100. The firstsubstrate 100 comprises an interposer comprised of an insulatingmaterial or glass in some embodiments. In other embodiments, the firstsubstrate 100 comprises a semiconductive material such as asemiconductor wafer. The first substrate 100 may include electroniccomponents and elements formed thereon in some embodiments, oralternatively, the first substrate 100 may be free of electroniccomponents and elements.

Bond pads and/or traces 103 comprising openings in wiring of the firstsubstrate 110 are formed on the top surface of the first substrate 100in a peripheral region of the first substrate 100 in a top view. Bondpads and/or traces 112 comprising openings in wiring are formed on thetop surface of the first substrate 100 in a central region of the firstsubstrate 100 in a top view. Bond pads and/or traces 103 and are shownin a more detailed view in FIG. 9. Bond pads 146 (not shown in FIG. 1;see FIG. 2) are formed on the bottom surface 144 of the first substrate100. The bond pads 146 may be arranged in an array or in rows or columnson the bottom surface 144 of the first substrate 100, not shown. Thebond pads 146 may fully populate the bottom surface 144 or may bearranged in various patterns, such as patterns used in ball grid array(BGA) or land grid array (LGA) package devices, as examples. The bondpads and/or traces 103 and 112 and bond pads 146 comprise a conductivematerial such as Al, Cu, Au, alloys thereof, other materials, orcombinations and/or multiple layers thereof, as examples. Alternatively,the bond pads and/or traces 103 and 112, and bond pads 146 may compriseother materials.

The first substrate 100 may optionally include a plurality ofthrough-substrate vias (TSVs) (not shown) formed therein in someembodiments. The TSVs comprise a conductive or semiconductive materialthat extends completely through the first substrate 100 may optionallybe lined with an insulating material. The TSVs provide verticalelectrical connections (e.g., y-axis connections in the view shown inFIG. 1) from a bottom surface to a top surface of the first substrate100.

The first substrate 100 includes wiring 156 (see FIG. 9) formed withinone or more insulating material layers. The wiring 156 provideshorizontal electrical connections (e.g., x-axis connections in the viewshown in FIG. 1) in some embodiments, for example. The wiring 156 mayinclude fan-out regions that include traces of conductive material forexpanding the footprint of the first die 110 to a footprint of thebottom side 144 of the first substrate 100, e.g., of the bond pads 146.The wiring 156 of the first substrate 100 may include one or moreredistribution layers (RDLs). The RDLs may comprise one or moreinsulating layers and wiring layers. The RDLs may include inter-leveldielectrics (ILDs) with wiring in metallization layers disposed orformed therein. The wiring 156 may comprise one or more vias and/orconductive lines, for example. The wiring 156 and the TSVs may be formedin the first substrate 100 using one or more subtractive etch processes,single damascene techniques, and/or dual damascene techniques, asexamples. A portion of the wiring 156 may reside on the top and bottomsurfaces of the first substrate 100; e.g., portions of the wiring 156 ofthe first substrate 100 may comprise the bond pads and/or traces 103 and112 and bond pads 146 that are coupleable to other elements.Alternatively, the bond pads and/or traces 103 and 112 and bond pads 146may be formed separately and attached to portions of the wiring 156, inother embodiments.

Referring again to FIG. 1, in accordance with embodiments of the presentdisclosure, a plurality of metal pillars 102 is attached to the bondpads and/or traces 103 on the top surface of the first substrate 100.The plurality of metal pillars 102 is formed using a two-step platingprocess, to be described further herein. The metal pillars 102 include afirst portion 104 and a second portion 106 coupled to the first portion104. The height of the first portion 104 in a vertical direction isthinner than the height of the second portion 106. The first portion 104is disposed directly over the bond pads and/or traces 103. The secondportion 106 is coupled to and disposed directly over the first portion104 of each metal pillar 102. The metal pillars 102 comprise a heightcomprising dimension d₁ of about 200 μm or less in some embodiments. Inother embodiments, dimension d₁ may comprise about 90 to 190 μm, asanother example. The metal pillars 102 comprise a width comprisingdimension d₂ of about 10 to 250 μm in some embodiments. Alternatively,dimensions d₁ and d₂ may comprise other values.

The plurality of metal pillars 102 comprises a conductive material, suchas a metal. In some embodiments, the plurality of metal pillars 102comprises Cu. In other embodiments, the metal pillars 102 (e.g., thefirst portion 104 and the second portion 106 of the metal pillars 102comprise Cu; a Cu alloy; a combination of Cu, Ni, and solder; acombination of Cu and solder; and/or combinations thereof, for example.The metal pillars 102 may comprise a column shape, a cone shape, aladder shape, a socket shape, a shape of a letter “I”, or a shape of aletter “T” in a cross-sectional view, to be described further herein.The metal pillars comprise a column shape in FIGS. 1 and 2, for example.Alternatively, the metal pillars 102 may comprise other conductivematerials and/or metals and the metal pillars 102 may comprise othershapes. The formation of the metal pillars 102 and additional dimensionsthereof will be described further herein with reference to FIGS. 9through 15.

Referring again to FIG. 1, the first die 110 is attached to the firstsubstrate 100. The first die 110 comprises an integrated circuit or chipthat will be packaged with a second die 128 a and optionally also athird die 128 b (not shown in FIG. 1; see FIG. 27) in a single PoPdevice 142. The first die 110 may include a workpiece that includes asemiconductor substrate comprising silicon or other semiconductormaterials and may be covered by an insulating layer, for example. Thefirst die 110 may include one or more components and/or circuits formedin and/or over the workpiece, not shown. The first die 110 may includeconductive layers and/or semiconductor elements, e.g., transistors,diodes, capacitors, etc., also not shown. The first die 110 may compriselogic circuitry, memory devices, or other types of circuits, asexamples. The first die 110 may include a plurality of contacts (notshown) formed on a bottom surface thereof.

A plurality of bumps 114 may be formed on the bottom surface of thefirst die 110, e.g., on the plurality of contacts on the bottom surfaceof the first die 110. The bumps 114 may comprise microbumps and thebumps 114 may each include a solder cap 116 formed thereon, as examples.The bumps 114 are also referred to herein as conductive bumps. The bumps114 on the first die 110 are then attached to the bond pads and/ortraces 112 on the top surface of the first substrate 100, as shown inFIG. 1. A solder reflow process is used to reflow the solder caps 116 onthe solder bumps 114 and attach the first die 110 to the first substrate100, electrically and mechanically attaching the bumps 114 to the bondpads and/or traces 112 of the first substrate 100, for example. Thebumps 114 may alternatively be attached to the first substrate 100 usingother methods. In some embodiments, the first die 110 is attached to thefirst substrate 100 using a flip-chip bond-on-trace (BOT) attachmenttechnique. Alternatively, other flip-chip attachment techniques andother types of bond pads and/or traces 112 may be used.

The first substrate 100 is then singulated from other first substrates100 on the workpiece, forming a first packaged die 120. The firstpackaged die 120 is also referred to herein in some embodiments as abottom packaged die, for example. In some embodiments, the bottompackaged die 120 includes a plurality of solder balls 148 formed on bondpads 146 on the bottom surface 144 thereof, as shown in FIG. 2. Each ofthe plurality of metal pillars 102 is bonded to a bond pad and/or trace103 on the top surface 101 of the bottom packaged die 120. Final testsare then performed on the first packaged die 120.

A second packaged die 140 is next provided. A cross-sectional view of asecond packaged die 140 that includes a second die 128 packaged with asecond substrate 122 is shown. Details of the second packaged die 140are not shown in FIGS. 1 and 2; see FIG. 27. The second packaged die 140includes the second die 128 disposed over the second substrate 122, anda bottom surface 124 including a plurality of bond pads 134 formedthereon. A molding compound 130 may be formed over the second die 128 ata top surface 126 thereof. The bond pads 134 comprise substantially thesame footprint or layout as the metal pillars 102 on the first packageddie 120. A plurality of solder balls 132 is formed on the bond pads 134in the embodiment shown in FIGS. 1 and 2. An insulating material 136 mayoptionally be formed between portions of the solder balls 132 and overexposed portions of the bond pads 134, as shown.

After the plurality of solder balls 132 is formed on the bottom surface124 of the second substrate 122, the second substrate 122 is thensingulated from other second substrates 122 on a workpiece (e.g.,comprising a workpiece or strip of second substrates 122) the secondsubstrate 122 was fabricated on, forming a second packaged die 140.Final tests are performed on the second packaged die 140.

The second packaged die 140 is lowered until the solder balls 132 arecoupled to the metal pillars 102. Each of the plurality of metal pillars102 on the top surface 101 of the first substrate 100 (e.g., comprisinga bottom substrate) is coupled to a solder ball 132 on the bottomsurface 124 of the second substrate 122 (e.g., comprising a topsubstrate). The solder balls 132 are reflowed, so that a solder joint132′ is formed on each of the metal pillars 102 proximate the secondpackaged die 140, as shown in FIG. 2, which is a cross-sectional view ofa PoP device 142 packaged in accordance with an embodiment. The solderjoints 132′ have a substantially barrel shape in the cross-sectionalview. A solder joint 132′ is formed on a portion of each of theplurality of metal pillars 102. Each of the plurality of metal pillars102 is at least partially embedded in a solder joint 132′ at a topregion of the second portion 106. The solder joint 132′ may also extendover a portion of or over the entire first portion 104 of the metalpillars 102 in some embodiments, not shown in the drawings. Theplurality of metal pillars 102 is disposed between the first packageddie 120 and the second packaged die 140, as shown. The solder joints132′ electrically couple together the bond pads and/or traces 103 of thefirst packaged die 120 and the contacts 134 of the second packaged die120, and also mechanically couple together the first and second packageddies 120 and 140.

Before the first packaged die and the second packaged die are attached,an optional underfill material 150 may be applied under the first die110, between the first substrate 100 and the first die 110, as shown inphantom in FIG. 2. The underfill material 150 is applied using adispensing needle along one or more edges of the first die 110, forexample, although other methods may also be used to form the underfillmaterial 150. The underfill material 150 comprises epoxy or a polymer insome embodiments, although other materials may alternatively be used.

A molding compound 152 may also optionally be formed between the firstpackaged die 120 and the second packaged die 140, also shown in phantomin FIG. 2. The molding compound 152 may be formed after the firstpackaged die and the second packaged die 140 are attached.Alternatively, the molding compound 152 may be applied at least betweenthe metal pillars 102 before the first packaged die 120 and the secondpackaged die 140 are attached, to be described herein with reference toFIGS. 8, 18, and 19. The molding compound 152 may comprise similarmaterials described for the underfill material 150, for example.Alternatively, the molding material 152 may comprise other materials.The underfill material 150 may comprise a first molding compound that isformed over sidewalls of the first die 110, and the molding compound 152may comprise a second molding compound that is formed over the firstmolding compound 150 and the first die 110, in some embodiments, forexample.

A plurality of solder balls 148 may optionally be formed on the bottomsurface of the first substrate 100, as shown in FIG. 2. The solder balls148 are attached to the bond pads 146 on the bottom of the firstsubstrate 100, before or after singulating the individual packaged dies120, for example. The solder balls 148 may be formed using a ball mountprocess, followed by a solder reflow process, for example. The solderballs 148 may alternatively be formed using other methods.

In the embodiment shown in FIG. 2, the metal pillars 102 are formed on afirst packaged die 120 that comprises a bottom packaged die, and solderballs 132 are formed on a second packaged die 140 that comprises a toppackaged die. Alternatively, the metal pillars 102 may be formed on afirst packaged die 120 that comprises a top packaged die, as shown inFIG. 3, which shows a cross-sectional view of a PoP device 142 packagedin accordance with another embodiment. Solder balls 132 (not shown inFIG. 3; see solder ball 132 in FIG. 1 and solder joint 132′ in FIG. 3after a reflow process of a solder ball 132) are formed on a secondpackaged die 140 that comprises a bottom packaged die. Each of theplurality of metal pillars 102 on the bottom surface of the firstsubstrate 100 (e.g., comprising a top substrate) is coupled to a solderball 132 on the top surface of the second substrate 122 (e.g.,comprising a bottom substrate). The solder balls 132 become solderjoints 132′ after a solder reflow process to attach the first and secondpackaged dies 120 and 140 together.

In another embodiment, metal pillars may be disposed on both packageddies 120 and 140. For example, FIG. 4 is a cross-sectional view of a PoPdevice 142 packaged in accordance with another embodiment, wherein metalpillars 102 a and 102 b are disposed on both the first and secondpackaged dies 120 and 140, respectively. Metal pillars 102 a are alsoreferred to herein as first metal pillars 102 a, and metal pillars 102 bare also referred to herein as second metal pillars 102 b. A solder ball132 (not shown in FIG. 4; see solder ball 132 in FIG. 1 and solder joint132″ in FIG. 4 after a reflow process of a solder ball 132) is formed oneach of the plurality of first metal pillars 102 a or on each of theplurality of second metal pillars 102 b. A solder ball 132 mayalternatively be formed on each of the plurality of first metal pillars102 a and on each of the plurality of second metal pillars 102 b, forexample. Each of the plurality of first metal pillars 102 a is coupledto one of the plurality of second metal pillars 102 b using a solderball 132 formed on one of the plurality of first metal pillars 102 aand/or a solder ball 132 formed on one of the plurality of second metalpillars 102 b, and a solder reflow process is performed, forming thesolder joints 132″ shown in FIG. 4.

In the embodiments shown in FIGS. 1 through 4, the metal pillars 102,102 a, and 102 b comprise a column shape. FIGS. 5 through 8 illustratevarious alternative shapes of the metal pillars 102 in accordance withother embodiments. The shapes of the metal pillars 102 may be controlledusing photolithographic processes of layers of photoresist (see FIGS. 10through 12 at 158 and 152) prior to a plating process used to form themetal pillars 102. FIG. 5 illustrates a cross-sectional view of a PoPdevice 142 packaged in accordance with an embodiment wherein the metalpillars 102 comprise a cone or ladder shape. The metal pillars 102 arewider at the bottom than at the top. The sidewalls of the metal pillars102 may be substantially straight, forming a cone shape, as shown inFIG. 5. Alternatively, the sidewalls of the metal pillars 102 may bestair-stepped and have a ladder shape, as shown in FIG. 6, which is amore detailed view of a metal pillar 102 shown in FIG. 5.

FIG. 7 shows a cross-sectional view of a PoP device 142 packaged inaccordance with another embodiment, wherein the metal pillars 102comprise a socket shape. The socket shape of the metal pillars 102 has asecond portion 106 with a narrower top region that facilitates adheringwith a solder ball 132. Portions of the solder joint 132′ form aroundedges of the narrower top region of the second portion 106 of thesocket-shaped metal pillars 102 after a reflow process.

FIG. 8 is a cross-sectional view of a PoP device packaged in accordancewith yet another embodiment, wherein the metal pillars 102 comprise theshape of the letter “I”. The I shape of the metal pillars 102 also has asecond portion 106 with a narrower top region that facilitates adheringwith a solder ball 132. Portions of the solder joint 132′ form aroundedges of the narrower top region of the second portion 106 of the metalpillars 102. The solder ball 132 can be printed from a solder film ormay comprise a smaller-sized ball than in other embodiments describedherein, as examples. If the metal pillar 102 critical dimension (CD) issubstantially the same as the solder ball 132 diameter or solder filmwidth, the metal pillars can form an “I” shape, for example.

FIG. 8 also illustrates an optional protective material 154 (see alsoFIGS. 16 through 18, to be described further herein) that may be formedover top surfaces and sidewalls of the metal pillars 102 before couplingtogether the first and second packages dies 120 and 140. The protectivematerial 154 comprises a conductive or organic material that remains atleast on sidewalls of the metal pillars 102 after the solder reflowprocess to form the solder joints 132′. A portion of the protectivematerial 154 may also remain at a top surface of the metal pillars 102after the solder reflow process, as shown in FIG. 8.

Also shown in FIG. 8 is a molding compound 152 which is formed betweenthe first packaged die 120 and the second packaged die 140. The moldingcompound 152 is formed over the first packaged die 120 before couplingtogether the first and second packages dies 120 and 140. Portions of themolding compound 152 are removed from a top region of the metal pillars102 (see the embodiment shown in FIG. 26 and the description thereof) sothat electrical and mechanical connections may be made to the solderballs 132 to form the solder joints 132′.

FIG. 8 further illustrates a plurality of contacts 155 formed on thefirst substrate 100 that are formed in a central region of the firstsubstrate 100. The contacts 155 may optionally be formed simultaneouslywith the formation of first portions 104 of the metal pillars 102 in afirst plating process accordance with some embodiments (to be describedfurther herein with reference to FIGS. 9 through 13). The solder caps116 on the first die 110 are coupled to the contacts 155 of the firstsubstrate 100 in these embodiments, as shown. Each of the plurality ofconductive bumps 114 is coupled to one of the plurality of contacts 155in the central region of the substrate 100 by a solder cap 116.

FIGS. 9 through 13 illustrate cross-sectional views of a method offorming the novel metal pillars 102 using a two-step plating process inaccordance with an embodiment of the present disclosure. A firstsubstrate 100 previous described herein is first provided. A view of aportion of half of the first substrate 100 is shown that corresponds toa left side of FIG. 1. A more detailed view of the first substrate 100is shown. Wiring layers 156 comprising conductive lines and/or viasformed in one or more insulating layers are disposed proximate a topsurface of the first substrate 100. The wiring layers 156 may includeone or more redistribution layer (RDLs) and may include under-ballmetallization (UBM) structures, as examples. The wiring layers 156 mayalternatively comprise a plurality of traces of conductive materialformed in one or more conductive material layers of the substrate 100,as another example. Exposed portions of the wiring layers 156 comprisethe bond pads and/or traces 103 and 112.

A first plating process 163 (see FIG. 10) is used to form first portions104 of the metal pillars 102. In the first plating process, a firstlayer of photoresist 158 is formed over a surface (e.g., a top surface101 in the embodiment shown) of the first substrate 100, as shown inFIG. 9. A plurality of first patterns 160 a is formed in the first layerof photoresist 158 in the perimeter region of the surface 101 of thefirst substrate 100 using a first lithography process, as shown in FIG.10. The first lithography process may comprise directly patterning thefirst layer of photoresist 158 using a laser or other energy beam insome embodiments. In other embodiments, the first lithography processmay comprise patterning the first layer of photoresist 158 by exposingthe first layer of photoresist 158 to light or energy transmittedthrough or reflected from a lithography mask (not shown) having adesired pattern thereon. The first layer of photoresist 158 is thendeveloped, and exposed (or unexposed, depending on whether the firstlayer of photoresist 158 comprises a positive or negative resist)portions of the first layer of photoresist 158 are ashed and removed,leaving the portions of the first layer of photoresist 158 shown in FIG.10 left remaining. The first patterns 160 a in the first layer ofphotoresist 158 are disposed over bond pads and/or traces 103 of thewiring layer 156.

In some embodiments, as shown in the embodiment illustrated in FIG. 8,contacts 155 may optionally be formed in a central region simultaneouslywith the formation of first portions 104 of the metal pillars 102 in thefirst plating process. To form the contacts 155, a plurality of secondpatterns 160 b is also formed in the first layer of photoresist 158 inthe central region of the surface 101 of the first substrate 100 in thefirst lithography process, as shown in FIG. 10. The second patterns 160b in the first layer of photoresist 158 are disposed over the bond padsand/or traces 112 of the wiring layer 156.

A plurality of first portions 104 of the plurality of metal pillars 102is formed in the plurality of first patterns 106 a in the first layer ofphotoresist 158 using a first plating process 163, as shown in FIG. 10.A plurality of contacts 155 is also optionally simultaneously formed inthe plurality of second patterns 106 b in the first layer of photoresist158 in the first plating process 163, also shown in FIG. 10. The firstplating process 163 may comprise an electroplating process or anelectro-less plating process, as examples. Alternatively, other types ofplating processes may be used.

A second layer of photoresist 162 is formed over the plurality of firstportions 104 of the plurality of metal pillars 102, the contacts 155,and the first layer of photoresist 158, as shown in FIG. 11. A pluralityof second patterns 164 is formed in the second layer of photoresist 162using a second lithography process, as shown in FIG. 12. Each of theplurality of second patterns 164 formed in the second layer ofphotoresist 162 is disposed over one of the plurality of first portions104 of the plurality of metal pillars 102.

A plurality of second portions 106 of the plurality of metal pillars 102is formed in the plurality of second patterns 164 in the second layer ofphotoresist 162 using a second plating process 165, also shown in FIG.12. The second plating process 165 may comprise an electroplatingprocess or an electro-less plating process. The second plating process165 may comprise the same type or a different type of plating processthan the first plating process 163, for example. The second portions 106may partially fill the second patterns 164 in the second layer ofphotoresist 162, or the second portions 106 may substantially completelyfill the second patterns 164 in the second layer of photoresist 162, asshown in phantom.

In accordance with embodiments, the shapes of the metal pillars 102 maybe controlled by adjusting and selecting various parameters ofphotolithographic processes used to pattern the layers of photoresist158 and 162 prior to the plating processes 163 and 165 used to form themetal pillars 102. For example, photo processes such as a beam focus andan exposure energy of the second lithography process used to form thesecond patterns 164 in the second layer of photoresist 162 may becontrolled in accordance with embodiments to form second patterns 164that achieve the column shape, cone shape, ladder shape, socket shape,“I” shape, or “T” shape of the second portion 106 of the metal pillars102 in a cross-sectional view. When the second plating process 165 isused to fill the well-controlled second patterns 164, the metal pillars102 fill the shape of the second layer of photoresist 162, forming thedesired patterns of the metal pillars 102. Likewise, the shape of thefirst portions 104 of the metal pillars 102 may be controlled to achievedesired shapes.

The second layer of photoresist 162 and the first layer of photoresist158 are then removed as shown in FIG. 13, e.g., using a resist stripprocess. The shape of the metal pillar 102 formed by the first portion104 and the second portion 106 comprises a shape of a letter “T” that isinverted in this example. The first portion 104 has a height comprisingdimension d₃, wherein dimension d₃ comprises about 1 to 60 μm. Thesecond portion 106 has a height comprising dimension d₄, whereindimension d₄ comprises about 50 to 150 μm. Dimensions d₃ and d₄ mayalternatively comprise other values. The total height of the metalpillar 102 comprises a dimension d₁ that is about equal to d₃+d₄. Thefirst portion 104 has a width comprising dimension d₂, and the secondportion 106 has a width comprising dimension d₅, in this embodiment,wherein dimension d₂ is larger than dimension d₅. In other embodiments,dimension d₅ may be substantially the same as dimension d₂, such as theembodiments shown in FIGS. 1 through 4.

FIGS. 14 and 15 are cross-sectional views of an example of a method offorming a second layer of photoresist 162 over a first layer ofphotoresist 158 and a first portion 104 of the metal pillars 102 (andoptionally over the contacts 155) in accordance with an embodiment. Thesecond layer of photoresist 162 may comprise a dry film photoresist(DFR), although alternatively, the second layer of photoresist 162 maycomprise others types of resists. In embodiments wherein the firstplating process 163 does not completely fill the first patterns 160 aand second patterns 160 b, voids may form above the first portions 104and the contacts 155 when applying the second layer of photoresist 162,particularly at corners proximate the first layer of photoresist 158where there is a step height. To avoid such void formation, in someembodiments, the second layer of photoresist 162 is applied in thepresence of a vacuum 166, as shown in FIG. 14. A roller 168 is used toapply pressure to a top surface of the second layer of photoresist 162while rolling the roller 168 in a direction 170 in the vacuum 166ambient, as shown in FIG. 15, laminating the second layer of photoresist162 to the underlying materials. Rolling the second layer of photoresist162 in the presence of the vacuum 166 advantageously results in no voidsbeing formed over the top surfaces of the first portions 104, thecontacts 155, and the first layer of photoresist 158, and also resultsin improved photolithography results.

In some embodiments, the first layer of photoresist 158 comprises a wetphotoresist. The use of the vacuum 166 ambient is advantageous in theseembodiments, because the second layer of photoresist 162 comprising aDFR may be placed close to the first layer of photoresist 158, and thevacuum 166 may be allowed to pull the second layer of photoresist 162onto the first layer of photoresist 158 without contacting the secondlayer of photoresist 162, after which the roller 168 is used, achievinga very close contact of the second layer of photoresist 162 onto thefirst portions 104, the contacts 155, and the first layer of photoresist158.

FIGS. 16 through 18 illustrate cross-sectional views of methods offorming a protection layer 154 over the metal pillars 102 and forming amolding compound 152 over the metal pillars 102 and the first die 110 inaccordance with embodiments. The optional protection layer 154 comprisesa material such as Sn, Au, CuGe, Cu, Ni, Pd, an organic solderabilitypreservative (OSP), or combinations thereof, as examples. The protectionlayer 154 may be formed in some embodiments using an immersion process,such as an immersion tin (Sn) process or an OSP process. The protectionlayer 154 may also be formed by an electroless process, such as anelectroless nickel immersion gold (ENIG) process or an electrolessnickel electroless palladium immersion gold (ENEPIG) process. Theprotection layer 154 may also be formed using a chemical vapordeposition (CVD) process, e.g., to form CuGe. The protection layer 154may comprise a thickness of about 10 μm or less, and may comprise about1 to 2 μm in some embodiments, depending on the materials and formationprocess. Alternatively, the protection layer 154 may comprise othermaterials, may be formed using other methods, and may comprise otherdimensions.

The protection layer 154 may optionally be formed over the metal pillars102 in the perimeter region of the substrate, and the protection layer154 may also be simultaneously formed over the contacts 155 in thecentral region of the substrate for the first die 110, as shown in FIG.16. In other embodiments, the protection layer 154 is formed only on themetal pillars 102, as shown in FIG. 17. To avoid forming the protectionlayer 154 on the contacts 155, the first die 110 is attached to thecontacts 155 on the substrate 100, and an underfill material 150 isapplied under the first die 110. Then, the protection layer 154 isformed over the sidewalls and top surfaces of the metal pillars 102 inthe perimeter region of the substrate 100. In embodiments wherein theprotection layer 154 is formed on the contacts 155 in the central regionof the substrate 100, the first die 110 is attached to the contacts 155having the protection layer 154 formed thereon, as shown in FIG. 18. Amolding compound 152 is then formed over the substrate 100, over thefirst die 110, and between the metal pillars 102 having the protectionlayer 154 formed thereon. The soldering process to attach the soldercaps 116 to the contacts 155 may result in the protection layer 154being removed or being absorbed into the solder joints formed during thesoldering process, as shown. Alternatively, the protection layer 154 mayremain on the top surface of the contacts 155.

The soldering process for the top surface of the metal pillars 102 in asubsequent processing step used to attach the metal pillars 102 to thesolder balls 132 on the second packaged die 140 may likewise result inthe protection layer 154 being removed from over the top surfaces of themetal pillars 102 or being absorbed into the solder joints 132′ or 132″formed during the soldering process. Alternatively, the protection layer154 may remain on the top surface of the metal pillars 102 after thesoldering process, as shown in the embodiment illustrated in FIG. 8.

The use of a molding compound 152 between the first packaged die 120 andthe second packaged die 140 is advantageous in some applications becausethe requirement for an underfill material 150 may be avoided.Alternatively, an underfill material 150 may also be used under thefirst die 110 when a molding compound 152 is used, as shown in theembodiment illustrated in FIG. 2.

FIGS. 19 through 21, FIGS. 25, and 26 show cross-sectional views ofmethods of forming the molding compound 152 over the metal pillars 102and the first die 110, and opening the molding compound 152 over themetal pillars 102 so that electrical connections can be made to themetal pillars 102 in accordance with embodiments of the presentdisclosure.

In FIG. 19, a first packaged die 120 is shown after a molding compound152 has been applied. The molding compound 152 may comprise a liquidmolding compound (LMC) in some embodiments, as an example.Alternatively, the molding compound 152 may comprise other materials.The molding compound 152 may comprise a top surface that issubstantially coplanar with a top surface of the first die 110.Alternatively, the molding compound 152 may reside over the top surfaceof the first die 110, as shown in phantom in FIG. 19. In either case, ifthe molding compound 152 resides over top surfaces of the metal pillars102 in the perimeter regions of the substrate 100, the molding compound152 needs to be removed so that electrical connections and mechanicalconnections can be made to solder balls 132 on the second packaged die140.

FIG. 20 illustrates one method of removing the molding compound 152 fromthe top surfaces of the metal pillars 102, wherein the openings 172 inthe molding compound 152 comprise a vertical shape. The openings 172 areformed by laser drilling the molding compound 152. The sidewalls 174 ofthe openings have a vertical shape in this embodiment. The openings 172may be slightly wider than the top surface of the metal pillars 102, asshown, or may comprise other dimensions, such as the substantially thesame as, or slightly smaller than the width of the top surface of themetal pillars 102.

FIG. 21 illustrates another method of removing the molding compound 152from the top surfaces of the metal pillars 102, wherein the openings 172in the molding compound 152 comprise a cambered or angled shape. Theopenings 172 are also formed by laser drilling the molding compound 152.The sidewalls 174 of the openings 172 have a cambered shape that may besubstantially smooth in this embodiment. Alternatively, the sidewalls174 of the openings 172 may have a ladder shape, as shown in a moredetailed view in FIG. 22, which illustrates a ladder shaped opening 172over a metal pillar 102 shown in FIG. 21. This opening 172 shape (andalso the other opening 172 shapes described and to be described herein)may be used to extend a moisture penetration path, e.g., to the metalpillars 102, in some embodiments, by designing the opening 172 so thatit is equal to or larger than a critical dimension (CD) of the metalpillar 102, to prevent joint necking.

For example, in FIG. 22, the metal pillar width is labeled 2L, whereinL=metal pillar width/2. FIGS. 23 and 24 illustrate laser drillingcalculations of various angles, to determine the angle Θ of the camberedsidewalls 174. The opening 172 sidewall 174 angle Θ is based on themetal pillar 102 CD and the solder ball 132 size on the second packageddie 140. For example, the opening 172 sidewall 174 angle Θ may becalculated using the geometry concept shown in FIG. 24, wherein angleα=angle β. Applying this geometrical concept to FIGS. 22 and 23, thesolder ball 132 radius r and L may be used to determine Θ using theequation:Θ=sin e ⁻¹which, applied to the dimensions in FIGS. 22 and 23, results in theequation:(L/r)=L/r(180/π),which equation may be used to determine an optimal angle Θ of thecambered sidewalls 174 of the opening 172, in this embodiment.Alternatively, the angle Θ may be determined using other methods.

FIG. 25 illustrates another method of removing the molding compound 152from the top surfaces of the metal pillars 102, wherein the openings 172in the molding compound 152 comprise a curved shape. The openings 172are again formed by laser drilling the molding compound 152. Thesidewalls 174 of the openings have an upwardly bowled shape in thisembodiment, similar to a shape of the solder ball 132 on the secondpackaged die 140 which advantageously also prevents moisturepenetration.

In other embodiments, the molding compound 152 may be opened from overthe metal pillars 102 using a chemical-mechanical polish (CMP) processand/or by grinding, so that a top surface of the metal pillars 102protrudes from above a top surface of the metal pillars 102, as shown inFIG. 26. This embodiment does not require drilling the molding compound152. An endpoint detector can be implemented in the CMP and/or grindingprocess to determine when the top surface of the metal pillars 102 hasbeen reached. The molding compound 152 may be recessed below the topsurface of the metal pillars 102 by a dimension d₆, wherein dimension d₆comprises about a few to several μm or less, as an example.Alternatively, dimension d₆ may comprise other values. The embodimentshown in FIG. 8 illustrates a first packaged die 120 wherein the moldingcompound 152 was removed from over the top surface of the metal pillars102 using this embodiment, as one example. In some embodiments,dimension d₆ may be equal to zero, wherein the top surface of themolding compound 152 is substantially coplanar with the top surfaces ofthe metal pillars 102, as another example. The CMP process or grindingprocess can be used to remove a portion of the molding compound 152 andform an air exit space between the first die 110 and the second packageddie 140 in some embodiments, for example.

FIG. 27 is an example of a second packaged die 140 in accordance with anembodiment that includes a plurality of top dies 128 a and 128 bpackaged over a second substrate 122. More details of the secondsubstrate 122 are also shown in FIG. 27. To package a single second die18 a or two or more second dies 128 a and 128 b, a second substrate 122is provided, which may comprise a substrate similar to the firstsubstrate 100 described herein and which may comprise similar materialsand components as the first substrate 100. The second substrate 122 maycomprise a plurality of second substrates 122 formed on a strip orworkpiece (not shown). The second substrate 122 may include TSVs 178 andwiring 180 similar to the TSVs and wiring 156 described for the firstsubstrate 100. The second substrate 122 includes contact pads 176 on thetop surface in a perimeter region and contacts 134 on the bottomsurface. The contact pads 176 and contacts 134 may comprise similarmaterials described for the bond pads and/or traces 103 and 112 and bondpads 146 of the first substrate 100, for example.

Next, a second die 128 a is provided, which may comprise a die similarto that described for the first die 110, for example. The second die 128a is attached to the top surface of the second substrate 122. The seconddie 128 a includes a plurality of contacts 182 a on a top surfacethereof in a perimeter region. The second die 128 a is attached to thetop surface of the second substrate 122 using a glue or adhesive, notshown. The second die 128 a is then electrically connected to the secondsubstrate 122 using wire bonds 184 a along two or more edges of thesecond die 128 a. The second die 128 a may be wire bonded along all fouredges to the second substrate 122, for example. The second die 128 a isattached to the top surface of the second substrate 122 by wire-bondingcontacts 182 a on a top surface of the second die 128 a to contact pads176 on the top surface of the second substrate 122 using the wire bonds184 a.

In some embodiments, only one second die 128 a is coupled to the secondsubstrate 122, and then a molding compound 186 is formed over the seconddie 128 a and top surface of the second substrate 122, not shown in FIG.27. In other embodiments, two second dies 128 a and 128 b are coupledover the second substrate 122, as shown in FIG. 27. A plurality ofsecond dies 128 a and 128 b (or three or more second dies, not shown)may be stacked vertically over one another, above the second substrate122, for example. In other embodiments, a plurality of second dies 128 aand 129 b (or three or more second dies) may be coupled horizontallyover the second substrate 122, not shown in the drawings.

The second die 128 b is also referred to herein as a third die. Thethird die 128 b is coupled over the second die 128 a, e.g., attached tothe top surface of the second die 128 a using a glue or adhesive.Contacts 182 b on a top surface of the third die 128 b are wire bondedusing wire bonds 184 b to contact pads 176 on the top surface of thesecond substrate 122. The third die 128 b is wire bonded to the secondsubstrate 122 similar to the wire bonding of the second die 128 a to thesecond substrate 122 described herein, for example. Two or more rows ofcontact pads 176 may be formed on the top surface of the secondsubstrate 122. The inner-most row of contact pads 176 is wire bonded tothe second die 128 a, and the outer-most row of contact pads 176 is wirebonded to the third die 128 b, as shown in FIG. 27. A molding compound186 is formed over the third die 128 b and exposed portions of thesecond substrate 122. The molding compound 186 comprises an insulatingmaterial that protects the wire bonds 184 a and 184 b, for example. Themolding compound 186 may comprise similar materials described for themolding compound 152, for example. Alternatively, the molding compound186 may comprise other materials.

In some embodiments, the second dies 128 a and 128 b are packaged on thesecond substrate 122 using a flip-chip wafer level packaging (WLP)technique and wire bonding process, for example. Alternatively, thesecond dies 128 a and 128 b may be packaged on the second substrate 122using other types of packaging processes.

In some embodiments, the second substrate 122 may not include an RDL inthe wiring 180. All or some of the x-axis or horizontal electricalconnections may be made using wire bonds 184 a and 184 b, in theseembodiments. In other embodiments, the second substrate 122 may includean RDL in the wiring 180, as another example. All or some of the x-axisor horizontal electrical connections may be made in the RDL in theseembodiments.

After the molding compound 186 is applied, a plurality of solder balls132 is formed on the bottom surface of the second substrate 122, e.g.,the solder balls 132 are coupled to the contacts 134, as shown in FIG.27. The second substrate 122 is then singulated from other secondsubstrates 122 on the strip or workpiece the second substrate 122 wasfabricated on, forming a second packaged die 140. Final tests areperformed on the second packaged die 140. Solder balls 132 of the secondpackaged die 140 are then attached to the metal pillars 102 on the firstpackaged die 120 described herein, forming a PoP package 142, as shownin FIGS. 2, 4, 5, 7, and 8.

FIG. 28 is a flow chart 190 illustrating a method of packaging multiplesemiconductor dies (i.e., first dies 110, second dies 128 a, andoptionally also third dies 128 b) in accordance with an embodiment ofthe present disclosure. In step 191, a first die 110 is coupled to afirst substrate 100. In step 192, first portions 104 of metal pillars102 are formed on the surface 101 of the first substrate 100. In step193, second portions 106 of the metal pillars 102 are formed over thefirst portions 104 of the metal pillars 102. In step 194, a second die128 is coupled to a second substrate 122. In step 195, the metal pillars102 are coupled to the second substrate 122.

In some embodiments, the second dies 128, 128 a, and 128 b describedherein comprise memory devices such as random access memories (RAM) orother types of memory devices, and the first die 110 comprises a logicdevice. Alternatively, the second dies 128 a and 128 b and the first die110 may comprise other functional circuitry. A different method may beused to attach the second dies 128, 128 a, and 128 b to the secondsubstrate 122 than is used to attach the first die 110 to the firstsubstrate 100. Alternatively, the same method may be used to attach thefirst die 110 to the first substrate 100 that is used to attach thesecond dies 128, 128 a, and 128 b to the second substrate 122.

In some embodiments, the second dies 128, 128 a, and 128 b are packagedusing a flip-chip WLP technique and wire bonding, and the first die 110is packaged using a flip-chip and BOT technique, as an example. Thesecond dies 128, 128 a, and 128 b may also be packaged using a flip-chipand BOT technique, as another example. Alternatively, the second dies128, 128 a, and 128 b and the first die 110 may be packaged using othermethods or techniques.

The underfill material 150 and/or the molding compound 152 shown in FIG.2 may optionally be included in all of the embodiments described herein,not shown in all of the drawings. The bond pads 146 and solder balls 148may also be included on the bottom of each PoP package 142 describedherein, also not included in each drawing. The various shapes of themetal pillars 102 described herein may alternatively be formed on a toppackaged die as described for the embodiment shown in FIG. 3 and/or mayalternatively be formed on both a top package die and a bottom packageddie, as described for the embodiment shown in FIG. 4. The protectionlayer 154 may be included or excluded on the metal pillars 102 or onboth the metal pillars 102 and the contacts 155 in each of theembodiments described herein. Furthermore, the various shapes ofopenings 172 in the molding compound 152 over the metal pillars 102described herein may be utilized with any of the various shapes of metalpillars 102 described herein.

Embodiments of the present disclosure include methods of packagingmultiple semiconductor devices (e.g., first dies 110, second dies 128 a,and optionally also third dies 128 b) in a single PoP device 142 usingnovel plated metal pillars 102 in the electrical connections (e.g., thesolder joints 132′ and 132″) between the first packaged dies 120 and thesecond packaged dies 140. Embodiments of the present disclosure alsoinclude PoP devices 142 that include the novel metal pillars 102described herein.

Advantages of embodiments of the disclosure include providing novelprocess methods for fine-pitch PoP packages 142 and innovative methodsfor PoP packaged die 120 and 140 interconnection using novel platedmetal pillars 102. The metal pillars 102 are formed using a noveltwo-step plating process. The plating processes 163 and 165 can bealtered as desired by packaging designers for different metal pillar 102shapes, such as a ladder shape, socket shape, I shape, and other shapesdescribed herein, which provide improved structural strength, eliminateor reduce the chance of lithography misalignment, and allow forimplementation of a finer pitch. The metal pillars 102 and packagingmethods achieve improved mechanical resistance and improvedelectromigration performance, resulting in fewer solder joint 132′ and132″ cracks after thermal stress or drop tests and reduced reliabilityproblems. The packaging processes described herein have a reducedthermal budget with fewer solder reflow steps (e.g., compared to solderball-to-solder ball joints), resulting in reduced defects (such as voidsand delaminations) and less contamination, such as out-gassing.

Improved package coplanarity is achievable by the use of the novelplated metal pillars 102. Coplanarity of less than about 6 μm across aninterface between the first package dies 120 and the second packageddies 140 for a 20×20 mm² PoP package 142 is achievable using the metalpillars 102 described herein, as an example. The solder joints 132′ and132″ easily reform their original solder ball 132 shape after the solderreflow process used to attach the second packaged dies 140 to the firstpackaged dies 120. The metal pillars 102 also result in reduced heatingbetween the top packaged dies 140 and the bottom packaged dies 120, byfunctioning as an additional inter-thermal heatsink.

The PoP packages 142 including the metal pillars 102 described hereinmay be produced with very low costs due to process simplification,providing a cost savings in the packaging process. The solder materialof the solder balls 132 may utilize a low alpha solder that emits areduced amount of alpha particles, further reducing manufacturing costsby not requiring a metal finish. The use of a low alpha solder for thesolder balls 132 also provides safer working conditions in the packagingenvironment and in fabrication facilities. Alpha counts of less thanabout 0.0002 counts per hour (cph)/cm² are achievable using thepackaging techniques and novel metal pillars 102 described herein, forexample.

The presence of portions of the metal pillars 102 in the solder joints132′ and 132″ facilitate in the prevention of bridging of adjacentsolder joints 132′ and 132″. The metal pillars 102 increase a bridgingwindow of the PoP packages 142, reducing or preventing shorts, improvingdevice yields, and allowing for the development of finer pitch PoPpackages 142. The novel PoP structures and designs described herein areeasily implementable in semiconductor device packaging process flows.The various features and advantages of the plated metal pillars 102 andpackaging methods described herein result in improved packagereliability and longer package lifetime.

In embodiments wherein the contacts 155 are formed simultaneously withthe first plated layer (the first portions 104 of the metal pillars102), further reduced costs are achieved, by avoiding an additionalmanufacturing step to form the contacts 155. The optional protectionlayer 154 protects the metal pillar 102 from oxidation and humidity, andprevents degradation of the metal pillar 102 from subsequentpost-thermal processing such as laser drilling and molding. Theprotection layer 154 also promotes adhesion to subsequently formedunderfill materials 150 and molding compounds 152, and preventsinter-metal compound (IMC) formation, such as Cu—Sn, in someembodiments.

In accordance with one embodiment of the present disclosure, a PoPdevice includes a first packaged die and a second packaged die coupledto the first packaged die. A plurality of metal pillars is coupled tothe first packaged die. Each of the plurality of metal pillars includesa first portion proximate the first packaged die and a second portiondisposed over the first portion. Each of the plurality of metal pillarsis coupled to a solder joint proximate the second packaged die.

In accordance with another embodiment, a PoP device includes a firstpackaged die and a second packaged die coupled to the first packageddie. A plurality of metal pillars is coupled to the first packaged die.Each of the plurality of metal pillars includes a first portionproximate the first packaged die and a second portion disposed over thefirst portion. Each of the plurality of metal pillars is coupled to asolder joint proximate the second packaged die. Each of the plurality ofmetal pillars comprises a shape of a letter “I” in a cross-sectionalview.

In accordance with yet another embodiment, a method of packagingsemiconductor dies includes coupling a first die to a first substrate,and forming a plurality of first portions of a plurality of metalpillars on a surface of the first substrate. A second portion of theplurality of metal pillars is formed over each of the plurality of firstportions of the plurality of metal pillars. The method includes couplinga second die to a second substrate, and coupling the plurality of metalpillars to the second substrate. Each of the plurality of metal pillarscomprises a shape of a letter “I” in a cross-sectional view.

Although embodiments of the present disclosure and their advantages havebeen described in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the disclosure as defined by the appendedclaims. For example, it will be readily understood by those skilled inthe art that many of the features, functions, processes, and materialsdescribed herein may be varied while remaining within the scope of thepresent disclosure. Moreover, the scope of the present application isnot intended to be limited to the particular embodiments of the process,machine, manufacture, composition of matter, means, methods and stepsdescribed in the specification. As one of ordinary skill in the art willreadily appreciate from the disclosure of the present disclosure,processes, machines, manufacture, compositions of matter, means,methods, or steps, presently existing or later to be developed, thatperform substantially the same function or achieve substantially thesame result as the corresponding embodiments described herein may beutilized according to the present disclosure. Accordingly, the appendedclaims are intended to include within their scope such processes,machines, manufacture, compositions of matter, means, methods, or steps.

What is claimed is:
 1. A package-on-package (PoP) device, comprising: afirst packaged die; a second packaged die coupled to the first packageddie; a plurality of metal pillars coupled to the first packaged die,each of the plurality of metal pillars comprising a first portionproximate the first packaged die and a second portion disposed over thefirst portion, and wherein each of the plurality of metal pillars iscoupled to a solder joint proximate the second packaged die; and aprotection layer disposed over sidewalls of each of the plurality ofmetal pillars.
 2. The device according to claim 1, wherein the pluralityof metal pillars comprises a column shape, a cone shape, a ladder shape,a socket shape, a shape of a letter “I”, or a shape of a letter “T” in across-sectional view.
 3. The device according to claim 1, wherein theplurality of metal pillars comprises a material selected from the groupconsisting essentially of Cu; a Cu alloy; a combination of Cu, Ni, andsolder; a combination of Cu and solder; and combinations thereof.
 4. Thedevice according to claim 1, wherein the plurality of metal pillars eachcomprises a width of about 10 to 250 μm.
 5. A package-on-package (PoP)device, comprising: a first packaged die comprising a first die coupledto a first substrate; a second packaged die coupled to the firstpackaged die, wherein an air-gap is disposed between the second packageddie and the first die; and a plurality of metal pillars coupled to aregion of the first substrate disposed outside a width of the first die,each of the plurality of metal pillars comprising a first portionproximate the first packaged die and a second portion disposed over thefirst portion, wherein each of the plurality of metal pillars is coupledto a solder joint proximate the second packaged die, and wherein each ofthe plurality of metal pillars comprises a shape of a letter “I” in across-sectional view.
 6. The device according to claim 5, furthercomprising a protection layer disposed over sidewalls of each of theplurality of metal pillars, wherein the protection layer comprises amaterial selected from the group consisting essentially of Sn, Au, CuGe,Cu, Ni, Pd, an organic solderability preservative (OSP), andcombinations thereof.
 7. The device according to claim 6, wherein thefirst die is coupled to the first substrate in a central region of thefirst substrate, wherein the first substrate comprises a plurality ofcontacts disposed in the central region, wherein the protection layer isdisposed over sidewalls of each of the plurality of contacts in thecentral region of the first substrate, and wherein the first die iscoupled to the plurality of contacts by a plurality of conductive bumps,each of the plurality of conductive bumps being coupled to one of theplurality of contacts.
 8. The device according to claim 5, wherein thefirst portions of the plurality of metal pillars comprise a height ofabout 1 to 60 μm, and wherein the second portions of the plurality ofmetal pillars comprise a height of about 50 to 150 μm.
 9. The deviceaccording to claim 5, wherein the solder joints partially encapsulatethe second portion of the plurality of metal pillars.
 10. Apackage-on-package (PoP) device, comprising: a first packaged diecomprising a first peripheral region, a second peripheral regionopposite the first peripheral region, and a central region between thefirst peripheral region and the second peripheral region; a plurality ofmetal pillars coupled to the first peripheral region and the secondperipheral region of the first packaged die, each of the plurality ofmetal pillars comprising a first portion proximal the first packageddie, and a second portion distal the first packaged die; a secondpackaged die coupled to the first packaged die; and a plurality ofsolder joints disposed between the second packaged die and the secondportion of the plurality of metal pillars, wherein a width of the firstportion of the plurality of metal pillars closest to the first packageddie is larger than a width of the second portion of the plurality ofmetal pillars farthest from the first packaged die.
 11. The deviceaccording to claim 10, the first packaged die further comprising aplurality of bond pads disposed in the first peripheral region and thesecond peripheral region of the first packaged die, wherein the firstportion of each of the plurality of metal pillars is coupled to a bondpad of the plurality of bond pads.
 12. The device of claim 10, whereinthe second portion of each of the plurality of metal pillars comprisestapered sidewalls.
 13. The device according to claim 10, wherein a widthof each of the plurality of metal pillars is in a range from about 10 μmto 250 μm.
 14. The device according to claim 10, wherein the pluralityof metal pillars comprises a cone shape, a ladder shape, a socket shape,or a shape of a letter “T” in a cross-sectional view.
 15. The deviceaccording to claim 10, wherein the plurality of solder joints partiallyencapsulates the second portion of the plurality of metal pillars. 16.The device according to claim 10, further comprising: a protection layerdisposed over sidewalls of each of the plurality of metal pillars. 17.The device according to claim 16, wherein the protection layer comprisesa material selected from the group consisting essentially of Sn, Au,CuGe, Cu, Ni, Pd, an organic solderability preservative (OSP), andcombinations thereof.
 18. The device according to claim 10, the firstpackaged die further comprising a first die disposed in the centralregion of the first packaged die, the first die being laterally adjacentto and spaced apart from the plurality of metal pillars.
 19. The deviceaccording to claim 18, further comprising: a molding compound at leastpartially encapsulating the plurality of metal pillars and the firstdie.
 20. The device according to claim 19, wherein a surface of thefirst die facing the second packaged die is substantially coplanar witha surface of the molding compound facing the second packaged die.